This invention relates to invalid hoists for use in lifting elderly or infirm people, hereafter referred to as users, from a sitting position to a substantially standing position, and vice versa.
Such hoists are known whose major operating component is a lifting jib which pivots in a vertical plane and carries a sling which is placed under the user's arms and around his back to lift or lower him by operating the jib. Knee engaging means is also provided against which the user's knees or upper shins are intended to engage whilst he is being lifted or lowered, so as to assist in controlling the path of movement of his body.
One disadvantage of these known hoists is that the path through which a user's upper body moves between sitting and standing positions tends to be very different from that followed by a user performing such a movement of his own volition, in particular in that at least the first part of such movement is substantially straight up vertically, rather than involving a substantial degree of forward movement of the upper body as is natural. This results in a vertical force equivalent to substantially the whole weight of the user's body being applied under the arms, and this can easily cause the arms to be lifted and the user to slide out of the sling unless he is able to employ substantial muscle power to stop this happening, specifically by lying back into the sling and firmly gripping the end region of the jib with his hands, and clearly there are many potential users who are not capable of doing this. Furthermore the application of a substantially vertical lift tends to lead to uncontrolled rotation of the user's body about the vertical during the initial, substantially vertical, part of the movement, because at that time little or no pressure is exerted by the user's body against the knee engaging means.